1. Field of the Invention
The present invention relates to a valve-operating mechanism in an engine, including a cam operated in association with a crankshaft, cam followers turnably carried on an engine body, so that their tip ends are in slidable contact with the cam, rocker arms integrally connected to the cam followers and turnably carried on the engine body coaxially with the cam followers so that their tip ends are connected to valves mounted in the engine body, and valve springs for biasing the valves in closing directions, whereby the rocker arms are operated in association with the urging of the cam followers by the cam to open the valves against biasing forces of the valve springs.
2. Description of the Related Art
A conventional valve-operating mechanism in an engine has been already proposed by the assignee of the present application (see Japanese Patent Application No. 2000-276459). In this mechanism, a cam of a relatively large diameter is disposed on one side of an engine body, and a rocker arm and a rocker shaft of a relatively small diameter are disposed immediately above the engine body, whereby the upward overhanging of the valve-operating mechanism can be suppressed to reduce the entire height of the engine, and in turn to provide the compactness of the engine.
In this valve-operating mechanism, however, the following has been found by the present inventors: the cam follower and the rocker arm are obliged to be disposed at a distance along a turning shaft for the structural reason; when the cam followers ride on a base-circle portion of the cam, and in response to the release of urging forces on the cam followers, the valves are closed by biasing forces of the valve springs, the rocker arms are then pushed upwards by the valves and are swung upwards, to apply a couple of forces over the axes of the cam followers and the rocker shafts; such couple of forces cause turning support portions of the cam followers and the rocker arms to chatter, resulting in the generation of an abnormal sound or a striking wear.
Accordingly, it is an object of the present invention to provide a valve-operating mechanism in an engine, wherein the couple of forces generated over the axis of the cam follower and the rocker arm due to the biasing force of the valve spring are offset in a valve-closing process, whereby the abnormal sound or the striking wear can be prevented from generating at the turning support portions of the cam follower and the rocker arm.
To achieve the above object, according to the present invention, there is provided a valve-operating mechanism in an engine, comprising a cam operated in association with a crankshaft, cam followers turnably carried on an engine body so that their tip ends are in slidable contact with the cam, rocker arms integrally connected to the cam followers and turnably carried on the engine body coaxially with the cam followers so that their tip ends are connected to valves mounted in the engine body, and valve springs for biasing the valves in closing directions, whereby the rocker arms are operated in association with the urging of the cam followers by the cam to open the valves against biasing forces of the valve springs, wherein auxiliary springs are connected to the cam followers for biasing and turning the cam followers in the same directions as directions in which the valve springs bias and turn the rocker arms through the valves in a process of closing the valves.
With this feature, a couple of forces in one direction are applied over the axis of the cam follower and the rocker arm by a biasing/turning force of the auxiliary spring on the cam follower, and offset or weakened a couple of forces applied over the axis of the cam follower and the rocker arm by biasing and turning the rocker arm through the valve by the valve spring in the valve-closing process. Thus, it is possible to avoid the chattering of the turning support portions of the cam followers and the rocker arms to prevent the generation of an abnormal sound or a striking wear.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.